The present invention relates to an optical switch. More specifically, the present invention relates to an optical switch suitable for an optical communication system, an optical memory unit, an optical processing unit, an optical recording unit, or an optical printer, etc, and in particular, to an optical switch suitable for an optical system in which multi-channel optical switches are required to perform switching of specific kinds of light.
In recent years, as optical communication technology advances, an optical switch, which provides a high speed response, excellent miniaturization, high integration, decreased power loss, and reduced signal attenuation, is required.
There have been hitherto known, as an optical switch, a one using a liquid crystal, or a one for displacing the position of an optical fiber with a mechanical unit using an electromagnet, a one using micro-mirrors, a one using a means for generating bubbles disclosed in JP-A-10-90735, or the like. In these optical switches, however, the following problems existed.
In the optical switch using a liquid crystal, the response speed was restricted since switching was performed based on the operation of changing the orientation of molecules, so that it was difficult to apply this optical switch to optical communication which requires high speed signal transmission. Moreover, there also existed such a problem that it showed reduced light-usage efficiency, that is, an increased power loss in the optical switch since it was necessary to use a polarizing plate.
In the optical switch for displacing the position of an optical fiber with a mechanical unit using an electromagnet, it was impossible to miniaturize the device, thereby making it difficult to satisfy the high integration requirements. Moreover, there also was such a problem that the power loss increased since the switching was carried out with the aid of the mechanical action obtained by using the electromagnet.
In the optical switch using micro mirrors, there was a problem that the production cost increased since the manufacturing process was complicated. Furthermore, there was such a problem that the signal attenuation, that is, increased power loss of the optical switch increased due to the control of the light propagating in air.
The optical switch using means for generating bubbles is a switch being provided with a waveguide substrate and a heater substrate by intersecting them with optical waveguides in fine slits wherein liquid-is filled, and the switch is used to switch optical transmission channels depending on whether or not a liquid exists at the intersection areas in the fine slits by bubble generation with micro-heaters.
The operation principle of this optical switch is that the light signal supplied to the waveguide passes through the intersection area when there is no input signal. The light signal supplied to the waveguide is deflected into the other optical waveguide and proceeds thereinto when there is an input signal since the light signal is reflected by an interface between a solid phase and a gaseous phase. The interface is formed at each intersection area by virtue of bubbles formed because the liquid with which the fine slit is filled is heated and locally boiled by the micro heater; this is because the refractive index of the liquid stored in the fine slits intersecting the optical waveguide is controlled so as to be substantially the same as that in the waveguide. The optical switch using the means for generating the bubbles permits fine structuring of the device and provides excellent response properties, thereby at present increasing an interest, in particular in its utilizability.
Nevertheless, there were the following problems in this optical switch due to the usage of the micro heater for generating the bubbles.
(1) An increased response speed caused an increase in the thermal power accumulated through the emitted heat radiation. This provided a change in the refractive index of the liquid filling the fine slits, so that the optical switch had an increased power loss.
(2) The liquid being stored in the fine slits was deteriorated due to the heat with elapse of time and therefore the power loss of the optical switch increased. This caused a limitation in the durability of the optical switch and it was necessary to employ a throwaway type liquid and a supporting mechanism for collecting, supplementing, and recycling the liquid, thereby not only increasing the production costs, but also enlarging the overall system itself.
(3) The consumptive electric power was large due to the operation of the micro heaters.
Accordingly, the object of the present invention is to solve the problems encountered in the conventional optical switch so as to provide an optical switch which ensures a reduced power loss even if the response speed is designed to be increased, and which further ensures low production costs, excellent durability, and less consumptive electric power.
An in-depth, extensive investigation regarding optical switches has been made and it has been found that the above object can be attained by the following means, and it resulted in the present invention.
Namely, there is provided, according to the present invention, an optical switch being disposed in intermediate positions of optical paths to define a channel of a light signal, characterized in that the optical switch is constituted of a cell member in whose interior cells are formed, and a waveguide member having fine slits. A gas is filled in said cells of which side walls are formed by piezoelectric/electrostrictive elements or antiferroelectric elements, and a liquid is filled in the fine slits, the cells and the fine slits being communicated to each other via a communicating hole. Optical waveguides are intersected at the fine slits, and the cells are disposed at the crossing locations, and the side walls are expanded/constricted by applying an electric field to the piezoelectric/electrostrictive elements or antiferroelectric elements which form the side walls of the cells, and a part of the gas stored in each cell is ejected at the corresponding intersection area from the communicating hole into the corresponding fine slit.
According to the present invention, it is desirable that the polarization field of the piezoelectric/electrostrictive elements or antiferroelectric elements is aligned in the same direction as the driving electric field, and it is further desirable that regarding the state of crystalline grains of the surfaces of the side walls forming a cell, the crystalline grains suffering damage inside the grains is less than 1%.
Moreover, there is provided, according to the present invention, a method for manufacturing, with a punch and die, an optical switch being constituted of a cell member in whose inside cells are formed and a waveguide member having fine slits, wherein the cells, whose side walls are formed by the piezoelectric/electrostrictive elements or the antiferroelectric elements, are filled with a gas, and the fine slits are filled with a liquid. The cells and the fine slits communicate to each other via a communicating hole, wherein optical waveguides are intersected at said fine slits, and said cells are disposed at the crossing locations, characterized in that said method comprises the steps of:
preparing a plurality of green sheets made of piezoelectric/electrostrictive elements or antiferroelectric elements;
performing a first substep for machining first slit apertures in a first green sheet with the punch, a second substep for raising the first green sheet in tight contact with a stripper in the state where the punch is not withdrawn from the first slit apertures, and a third substep for raising the punch in such a manner that the front end of the punch is withdrawn slightly from the lowest part of the first green sheet thus raised;
performing a fourth substep for machining second slit apertures in a second green sheet with the punch, a fifth substep for raising the second green sheet together with the first green sheet in the state where the punch is not withdrawn from the second slit apertures, and a sixth substep for raising the punch in such a manner that the front end of the punch is withdrawn slightly from the second green sheet thus raised; and
subsequently laminating a plurality of green sheets by repeating the fourth substep to the sixth substep, and then forming the piezoelectric/electrostrictive elements or antiferroelectric elements including a plurality of slits.